The present invention relates to an image display device for displaying images which uses a display member in which image data may be written and erased.
One typical approach for wide screen displaying of a document in which characters and graphics are printed is duplicating the document on a transparent film (for use with an overhead projector of OHP) and projecting it onto a screen in an enlarged scale. Another typical approach is photographing the document by use of a reversal film or slide film and projecting it onto a screen in an enlarged scale.
Such traditional approaches have various drawbacks as follows:
(1) When the screen size is increased, the luminous intensity is lowered to render information displayed illegible;
(2) Because the room has to be darkened during the display, it is hard for one to look at documents at hand;
(3) The use of an OHP results in an extra period of time necessary for the preparation of the special sheet; and
(4) The use of a slide projector also increases the period of time and cost required because the special slide film is indispensable. An optical wide screen display device of any of the above-described types is contradictory to the current trend toward office automation.
Meanwhile, in a conference and other occasions where a number of attendance are expected to look at the same information presented or discussed, a blackboard is used quite often as an information transmitting medium. A recent achievement in the realm of display art is an electronic display device, or so-called electronic blackboard, which solves various problems inherent in an ordinary blackboard such as that it cannot preserve information written thereon.
However, an electronic display device presently available is no more than an implementation which allows information to be written by a pen instead of a piece of chalk and, if desired, allows it to be reproduced in a hard copy. That is, information cannot be displayed on the device unless written by hand just as in an ordinary blackboard, so that the device fails to meet the need for multiple functions.